1. Field of the Invention
The present invention relates in general to radio frequency devices and in particular to methods and devices for coupling radio frequency energy from transmission lines.
2. Description of the Related Art
Until this invention, coaxial taps and couplers were installed by cutting and connectorizing RF cable using coaxial jumpers. The primary disadvantage of this methodology is the resulting excessive loss to the host cable. Stein et al, U.S. Pat. No. 5,729,184, subsequently taught that a tap can be used without connectorization; however, the Stein et al. invention still caused losses of over 1 dB to the host cable. Stein et al did mention the theoretical ability to devise taps with coupling losses up to 20 dB but did not describe a method for the manufacture of such devices.
What are needed are methods and devices embodying the ability to select the coupling loss and accompanying insertion loss in RF systems. In particular, such methods and devices should allow a wireless system not only to be tuned but also should also allow minimization of number of amplifiers required to RF illuminate a structure.
The present invention relates generally to devices which couple electromagnetic energy from one electromagnetic transmission medium to one or more other transmission media and more specifically to devices which couple radio frequency energy from a coaxial cable to other coaxial cables, antennae or other radiating devices. Further, the present invention relates to devices which couple radio frequency energy from a transmission medium to another transmission or radiating medium, with variable energy and inverse loss to the host cable.
The present invention also generally relates to a device packaging or enclosure method which protects the electrical components, allows for sealing against water or other contaminant intrusions, generally allows for connecting the device to a host cable while preventing rotation, and provides a means of electrically connecting the ground of one device to the ground of another device. The present invention further relates to a device which can be attached to a host cable without the need to cut and connectorize the cable.
The principles of this invention provide not only the ability to build couplers with coupling losses from below 10 dB to over 30 dB but for the manufacture of such devices. The construction of these devices provides extremely low insertion losses at all values of RF coupling losses. For example, a coupling device of the present invention with a coupling loss of 15 dB will have an insertion loss of less than 0.3 dB. A 20 dB loss device will have an insertion loss of less than 0.1 dB.
Therefore, it is an object of the invention to provide means of presenting a large impedance to the through line cable while extracting RF energy efficiently.
It is a further object of the invention to provide a technique to connect a device to a through line such that RF energy may be extracted at several frequencies.
Another object of the invention is to provide a method of extracting RF energy from a through line at several frequencies while minimizing the loss in the through line.
It is a further object of the invention to provide a technique to extract RF energy from a through line at varying levels depending upon need.
Another object of the invention is to extract energy at varying levels while causing an inverse loss to the through line. That is the higher the coupling loss from the through line to the output of the object of the invention, the lower the insertion loss to the through line.
Yet another object of the invention is to provide a technique that allows an output impedance of the device to match, as close as possible, the input/output impedance of an RF amplifier, an antenna or another transmission line.
A further object of the invention is to provide a means of extracting RF energy from a through line while creating minimum intermodulation products.
It is a further object of the invention to provide a technique to extract RF energy from a through line while providing a minimum of loss in the through line at other frequencies.
Another object of the invention is to provide a technique to attach the device to a through line and transferring the energy to the output of the device with the maximum efficiency, that is the minimum heating loss.
Yet another object of the invention is to provide a means of transferring energy from the through line to the output of the device such that the ratio of RF energy flow will be little affected by temperature, humidity and/or vibration.
A further object of the invention is to provide a means of inexpensively and efficiently assembling the device.
Another object of the invention is to provide a technique to manufacture or assemble a coupling device to respond to different frequencies, bandwidths, coupling losses and through line losses using preformed internal wiring.
Still another object of the invention is to accomplish the energy transfer using a variable impedance transmission line.
Yet another object of the invention is to provide a technique that couples energy from a through line to the output of the device using a single, bare conductive wire as the variable impedance transmission line.
Another object of the invention is to provide a means of controlling the energy coupled from a host cable to the output of the device by adjusting the distance and configuration of the wire from the connection to the host cable.
Yet another object of the invention is to provide a mechanical package to contain the electrical components.
Still another object of the invention is to provide a mechanical package that can be sealed to prevent water or other contaminants from degrading the electrical performance of the device.
Another object of the invention is to provide a device which can be connected to a host cable by drilling only one hole and placing the device on the cable and tightening 2 captive screws.